Manufacture of carbon black



Jan. 14, 1941. H. H. OFFUTT MANUFACTURE OF CARBON BLACK Original FiledJune 11, 1934 Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE uazzarloi u a autoito Godfrey L. Cabot, Inc Boston, Mass a corporation ofMassachusetts Application August 10, 1937, Serial No. 158,355,

which is asubstitute, for abandoned application SerlaiNo. 730.059, June11, 1984. Divided and this application June 22, 1938, Serial No.

11 7 (c1. as-sm) This invention relates to improvements in themanufacture of carbon black, and more particu-,

larly to a novel process of condensing or com- 2,167,674 flied Aug. 10,1937 which in turnis 8" substitute for my earlier application, 730,059,flledJune 11, 1934.

Set. No.

l Carbon black ,as first produced by combustion of natural gas is hardlymore than acolloidal suspension of flocks or carbon particles in air.

It has an apparent density in bulk of about 3 pounds per cubic foot andis light, flocculent, ad- 2o herent and dusty. On this. account, it isextremely difficult to pack, transport and handle in industry. Thegeneral object of the present invention is to provide a practical andeconomical process of converting carbon black of, this char- 2.) acterinto a substantially dustless and relatively dense granular form inorder to make it more convenient and economical in the respects notedand otherwise improve its characteristics for industrialuses. i 1

3o I have found that the flocculent, colloidal suspension of carbonblack particles in air may be converted to a much denser form if the airis replaced by water or other suitable liquid so as'to form a suspensionof carbonblack in .water,'oil

z.) or other suitable liquid by displacement. of the air under suitableconditions of operation.

I have also found that by overwetting a limited number of particles in amass of carbon black groups of wetted particles may be -ea'used'to 'actin as' nuclei and that when a mass containing flocculent carbon blackand such'wet'ted nuclei is stirred, the dry. flocculent black coheres tothe nuclei by impact. The excess of water in the nuclei then seeps outinto the coheringdry black is and the forces of surface tension and thephysico-chemical attractions of particle for'particle come into play,resulting in the formation of" stable agglomerates, suiiicientlytenacious to withstand transportation in bulk, substantially no dustlessand having an apparent density-in'bulk.

ofat '"least =12 pounds per cubic foot. tVarious wetting agents may beused. depending. upon the character of the product desired. For-example;granules of pure carbon black maybe produced 55 by wetting the nucleusparticles with water, agitating the and subsequently evaporating thewater from the granular product. Again, carbon black granules usefulinlthe manufacture of ink may be produced by using oil asa wettin a ent,and in thiscase it is not necessary to re-' 5 move the oil from thegranular product since this is a useful ingredient in inks. H

The type of apparatus or equipment used in carrying out the process isof secondary importance so long as it provides means for stirrin oragitating the carbon black mass soils to subject its particlestoturbulence and pressure and means for preventing caking which wouldresult in the formation of shear surfaces. One satisfactory apparatuscomprises a vertically-disposed;

cylindrical tank e ipped with a rotary agitating cage, stationary baillemembers, and a slow moving side and bottom scraper; another comprises ahorizontally-disposed rotary drum with a wall and end scraper, eachcontainer being provided with a nozzle for. spraying or otherwisesupplying measured amounts of liquid to the mass of dry carbon blackcontained vtherein'w'hile it is being a itated. v

I have found that with; the cheaper grades of 2 carbon black,particularly those used'b'y the rubber industry andv those used for thepurpose oi.- making news inks, that'thejei'iect of the additionofiwater' up to '1 part of water tol parts carbon black ishardlyfnoticeable, but that as water is added in an amount betweenll and1% parts of water to 1% parts of carbon black a pronounced change takesplace when the carbon black .is agitated. This is characterized by arapid decrease in volume and agglomeration of the flocculent carbonblack into" granules of varying sizes. As more water is added, thesegranules build up into solids of various sizes. This stage isdefinitelyterminated when water amounting to more than: 1% parts of water to 1part of carbon blackhas been added. Under these circumstances, themixture begins to partake of the 'nature of a dough or paste and thatcondition marks the upper limit of the working range in which Laminterested. The addition of water to an amount equal to the weight ofthe carbon black has the effect of-reducing its volume substantially andof rendering more .efiectivethe .mechanical work done in agitating thecarbon black'in course of treatment; w I

I have found that thesizesand shapes of gran-, ules depend to someextent upon the character of are admitted to the container. Ifthe liquidis added rapidly to. the carbon black in the container, spherical grainsas large as peas may be formed and, while such a product is of goodcommercial density and much less dusty than the heavy compressed carbonblack of commerce, it tends to break down into fragments of irregularshape and size when transported in bulk. Ac-

cordingly, it is 7 preferred to supply the, liquid slowly, as bydripping or atomizing, and thus to keep the granules always smaller insize, for example, below 40 mesh, in which are stableinstructure. I r

In making granules of pure carbon black, a preferable procedure is toatomize water in aflne mist upon the surface of flocculent carbonblackwhich is being stirred. Under these conditions,

an infinitely greater number of wetted nuclei is formed and,consequently, a greater number of granules is produced. Granulesprhduced by this procedure, when dried, are suitable for'immediateshipment in bulk without danger .of any considerable amount ofdisintegration. The product thus produced may-have an apparent densityin bulk of :upwards of pounds per cubic foot. If the agitating processis prolonged and a greater amount of work done uponthe carbon .black,the granules tend to become reduced in size and increased in density;Similar results may be secured by returning thedried granules to theagitating apparatus and continuing the agitating process. Under suchconditions, it is possible to raise the apparent density of the prodnotas high as or pounds per cubic'foot. When carbon black is to be used forthe manufaoture of ink, it is important that it shall be freefromfaggregates which'ofler resistance in the carbon black 111-;

.mass of carbon black in thin layers with oil accompanied by no morestirring than is 118083,- sary to present new surfaces for wetting. Theprocess may bestb'e carried out in' a horizontally disposed rotatingdrumwith side and end scraper provided with a nozzle for spraying measuredamounts of oil on theiiuffy freshly exposed surface of the carbon black.

Under these conditions, I have found that 2 parts of oil are required to1 part of carbon black yin order to produce a dustless, free-flowing,oilblack mixture of good commercial density for use in the manufactureof news ink. Mixtures of oil and black prepared in this manner possessthe new and novelfeature of containing none of the grit with which theink manufacturer-hasv had formerly to contend... As evidence of this, Ihave found that an ink made from the ordinary agitated, news-ink carbonblack will show area! due of .1% on a 300 mesh-screen, whereas an" inkmade from identical raw material by my new process will show a residueof .0l% only.

As'evidence of the absence of agglomerates of a size smaller "than300-mesh, I have found that commercial density and dustless,free-flowing size range they part jf'oil ,to 1 part'of carbon black.

' product is not "quite as satisfactory, although it an ink made fromtheiordinary agitated n w 1 ink carbon black will 'flow 12 inchesundrstandard procedure for flow test, whereas 'an ink made from my newproduct and containing the same percentage of carbon black will onlyflow -5 V inch. Stated otherwise, these figures prove a greatsuperiority in fineness of dispersion for the new products I have foundthat oil botanists good characteristics may be produced in averticallydisposed cylindrical tank equipped with a rotary agitatingcage, stationary'baille members, and aslow moving sideand" bottomscraper, using 1 Under" these conditions, the stirring is much moreeflicient thanin the example previously given. Consequently, the numberof chance dry adhesions is-greater and ink made from this is betterthanink'made from the ordinary agitated, news-ink carbon black.

Inorder to prevent objectionable dry adhesions and indispersibleaggregates, isadvisable that 11 no more stirringbe done than isnecessary to expose'fresh surfaces and that the oil film be dependedupon almost entirely for the condensation of the carbon'black. a I v Theproduct obtained by either of the abovementioned procedures consists ofsomewhat irregularly shaped spheroidal granules of carbon black and oilbonded together by the surface tension effects of the oil film and bythe inherent physico-chemical attraction of carbon black particle forcarbon black particle. However,

under the described conditions, the oil "film tendsto preventdryadhesions that are -dimc'iult orimpossible to break down during "the inkmanufacturing: process. Here, as before, the size and shape of thegranules depends upon the finenessof the drops of oil sprayed upon thecarbon black and the amount'of work done upon the These and otherfeatures of the invention will be best understoodand appreciated fromthe fol lowing description of a specific example of its application,illustrated in the accompanying drawing, in'which M I a Fig. 1 isa viewin perspective showing one suitable i'orm of apparatus, with portionsbroken away to show the mass of carbon black therein;- Fig. 2 representsspherical grains of carbon black granules as shown in the field of amicroscopemagnifled about 60 diameters: and

Fig. 3 is a sectional view of a-sin'gleispherical granule magnified 300diameters. The apparatus illustrated comprises a vertical ly-disposedcylinder or drum ll having a removable cover provided with a hand holell and a discharge chute I! in its bottom. Secured to the inner face ofthe cover I! is a disk It from which project downwardly aseries ofstationary bailie rods l0 arranged substantially concentrically inthedrum. .1 disk 2. is mounted for rotation near the bottmn of the drum andprovided with a series of upwardly-projecting, baiile rods 12 arrangedconcentrically in a circle outside the'stationary baiiie rods II. Therotatable disk 20 also carries a flat spiralband 24 which extends to apoint adjacent theupperends of the baille rods 22. Thedisk 2| is securedto and driven by a shaft 28 which is mounted in suitable bearingsbeneath-the bottom of the drumand provided at its lower end with apinion II by which it may be 1s rotated through any suitable geartrain,[Beneath the disk 2| is located a bottom scraper-3|,

and from the outer endof this extends an upright side scraper 32. Thebottom scraper 3| is se- 5 cured to and driven'by a sleeve 34 mounted insuitable bearings concentrically with respect to the shaft 26 andProvided with a driving gear wheel ll by which the scrapers may bedriven independently of and at a slower rate than'the cage formed by thedisk in and the bame rods 22. m

the upper part of the drum is provided an atomizing home. 31 supplied bya pipe 33' and eontrolled by a valve 33. i 7

One example of the manner in which theabove described apparatus may beused in carrying out the novel process of my invention is as follows.The drum is supplied with a charge of 100 pounds of carbon black of anyof the cheaper grades used in the manufacture of rubber or ink andhaving an apparent densityin bulk of about 3 pounds per cubicfoot. Themass of carbon black in the drum is indicated by reference character 40.The valve 39 is then adjusted to supply water at the.

rate of about 100 pounds in minutes, and powsurface of the carbon-blackmass. These wetted groups of particles act as nuclei upon which are;built up stableagglomerates of generally, sphe- I roidal formas theparticles of the whole carbon black mass are agitated and so subjectedto turbulence and pressure by the movement through it of the bailie rods22 and thespiral member 24.

The stationary baflle rods I! prevent movement .of the carbon black massas a whole and cause a general agitation and flowing of the particlesupon each other so that the wetted nuclei are" moved in the mass,brought into contact .with dry 5 particles, and turned so thattheytendto-build up systematically and progressively and formhomogeneous 'bodies held-together by the coherentforce of particle forparticle, surface tension of the ,water and other suri'ace effectswhichare notfully understood. The action of the scrapers i.

is to prevent caking of the carbon black upon the bottom and side wallsof the drum.

As the process proceeds, there is no apparent changein the mass bfcarbon black being treated until about 66 pounds of water has beensupplied by the nozzle 31. From this point on and until about 100 poundsof water has been supplied,

there is a very pronounced concentration. andcontraction of the"carbonblack mass and the gradual and increasing appearance therein ofspheroidal grains of 7 carbon black, as -distinguished from thefiocculent particles present at H thebeginnlng of the procedure.

At the end of about so minutesflwhen 1'00' pounds of water has beensupplied'through one or more atomizing nozzles as above outlined, thecharge may be drawn off and dried, and it will be found that theflocculent carbon black has entirely disappeared, having been convertedinto '70 granules more or less spheroidal in shape, be-

tween 100-mesh and 20-mesh in size and having an apparent density inbulk of about 15 pounds per cubic foot. This product is substantiallydustless, free flowing and suillciently tenacious of structure towithstand shipment in bulk without dusty disintegration. A small grainsize isgen erally to be preferred for shipping and if, instead of.drawing of! the charge 'as soon as converted, the process iscontinuedfor another 30 minutes. the granules become. reduced in size and 'in- 5creased in density to 20 pounds per cubic foot or 1 more. In general, Ihave found that between 40- mesh and GO-mesh' is the optimum size ofgranule for shipping. The converted granular charge may be convenientlydried in about 3 hours at 'a 10 I temperature of C. if spread in"alay'er about one-half inch thick. j I

In Fig. 2 I have shown thegeneral appearance of the carbon blackgranules as they appear in the field of a microscope, magnified about 60dimeters. at the conclusion of the process of treat-- ment abovedescribed. In Fig. 3 is represented a single granule in cross section.and from this it will be observed that thestructure of the entiregranule is homogeneous, without concentric shells or'irregularagglomerates of various densities. The resulting granulesare, of course,when dried of pure carbon black without the addition of any bindingmaterial andwhile they are individually tenacious enough to withstandtranspor tation in bulk they maybe easily broken down and dispersed, forexample in a rubber mix, by slight shearing orrubbing pressure.

In preparing an oil-carbon black mixture, the 30 same apparatus maybeusedand oil may be supplied in the form of a line mist by the nozzle31. The process proceeds asabove except that the amount of agitation isreduced to the and the final density of the product is somewhat less.fI'heoil-carbon black mixture and the proc; ess of making it arenot'herein-claimed,.but constitute the subject matter of .my 'copendingappliv cation above identified. The, apparatus herein shown is disclosedin U. s. Letters Patent n 2,121,535, granted 'June 21, 1938 on anapplication of F. H. Amon, to which reference may be had for furtherdetailsof' construction. It will be vunderstood,however, that suchapparatus is illustrative only and that many.

variations in treatment are within theIIscopeTof t the invention. Forexample, the oil orjliquid may be deliveredwithin the of flocculentcarbon: black and the latter may,'ji f "desired, be agitated 1 by fluidrather than'mechanical means. p

Having thus described my invention, '-what- I' cut is:

1. The process of compacting flocculent carbon black, which consists ingradually wetting only certain particles in a mass of carbon black tocause them to act asnuclei, continuing the 'wet ting stepluntil a weightof liquid has been added not less than 66% nor morethan of the weightofthe carbon black treated, and stir-"- ring the particles dfItheotherwise while preventing movement of the asa whole and thereby causing.other particles to cohere to the nuclei and thus to buildupsubstantiallydustless discrete granules directly from the treated massof carbonblack. v a

2. The processof compacting flocculent carbon" black, which consists ingradually spraying with water the surface of a mass of carbon blackhaving a density of approximately 3 pounds per cubic I foot, continuingthe spraying step until a weight 70 of water has been added not lessthan 66% nor more than 150% of the weight of the dry carbon blacktreated, stirring the particles of the otherwise dry carbon black whilepreventing movement of the mass as a whole and thereby building '1 claimas new and desireto secure by Letters Pat 7 of more than 15 pounds percubic foot.

up directly from and in the mass discrete granules about the wettedparticles as nuclei, and then drylngythegranules to i'orrn asubstantially dustlesssmn'ular product having an apparent density or atleast 15 pounds per cubic ioot.

1 3.-. Th e process of compactlngflf ulcnt carbon black,which consistsin gradually adding to,

thespraying step until a weight of liquid has been addednot lessthan66%"nor more than 150% of the weight 01' the drycarbon blacktreated, hold I ing theimass as afwhole at rest andmeanwhile stirringthe particles thereof to; causethe systematicand progressive buildingup'directly from the of 1 dry carbon particles upon wetted' nuclei 'irito"relatively dense coherent grains oi juniiorm structure, and then i'onnasubstantially dustless product.

- 5." The process of compacting flocculent carbon black, vwhich consistsin overwetting separatedgroups of particles in a oi otherwise'dry carbonblaclr having an apparent density in bulk of about 3 pounds per cubicfoot, thereby causing the v overwetted particles to'oohere and-formnuclei in t e n o which er d particles cohere, continuing the wetting sep, until 'a weight of liquid hasbecnadded not less than 68% nor morethan" 150% of the weight of 'the dry carbon black treated, holding themass as a'whole at rest and meanwhile agitating the particles thereof tosub- Ject thellnuclei to symmetrical pressure and to cause thecoherencethereto of additional particles, thus building up systematically andprogressivelyfdirectly from the treated mass spheroidal granules ofblack oi a density 6. The process of con erting flocculent carbon blackinto dense, non-adherent spherical granules,

which consists in overwetting only certain particles inn mass orotherwise dry carbon black and agitating the particles 01' the masswhile prevent ing movement thereof as a whole thereby causing a dryparticles to become wetted'and to cohere to the overwetted particles andform relatively dense nuclei, continuing the wetting step until a weightof liquid has been added not less than 66% nor more than 150%,0! theweight oi the dry carbon black treated, and then subjecting said nucleiand floccuient carbon black topressure and turbulence causing theflocculent particles to build up pro- -gressivel'y and continuouslydirectly from" the treated mass upon said nuclei into a mass ofdiscr'ete dustless granules. v

.'l.- The process of converting ilocculent carbon black having adensityof about 8 pounds per "cubic root into substantially spherical grainshavinga density oi at least 80 pounds cubic foot,

which consists in spraying the surface or a mass of flocculent carbonblock which is otherwise dry,

continuing theffspraying fstep Tuntil a I weight of liquid has beenadded not less than Ice nor more 150% of the weight of the dry carbon 1black treated and while the .mass as a whole is held against movementvsubjecting jits particles to turbulentragitatiom'therebyproducing a massoi 4 discrete, spherical granuleslhaving a density '0! about 12 poundspercubic' feet, then drying the product, and then" subiec'ting. thedried product to turbulent agttation 'and thereby'increasing its density'tosubstantially 30 pounds per 'cubioioot. f 8. The process ofcompacting nocculent carbon" blaclr. 4 which consists v in graduallywetting -only c t i Par icl s njammf carbon blakto cause them to act asnuc1ei,'oontinuingthe"wetting step until a weight oi liquid has beenadded not iess'than 88% normore than 150% 01 the" weight oi" the drycarbon-black treated, and stir-- ring the particles of the otherwise drymass and thereby cau l tnerfparticle's tocohere-to the v 1 nuclei, andthus'to buildupsubstantially dustless discrete granules directlyfrom-the treated mass '0! carbon blacku I q i 9. The'process-oi'compacting nocculent carbon black, which consistsingradually spraying liquid upon the surface or "a mass thereof,continuing 1'.

the spraying step until a weight'oi' liquid has been added not less than68% nor more than-150% of the weight of the dry carbon black treated,meanwhile stirring theparticles thereof tocause v the systematic andprogressive building up directly from the treatedmass'of dry carbonpar-,

ticles upon wetting nuclei into relatively dense coherent grains ofuniform structure, and then drying to. form asubstantially dustlessproduct.

10. 'lheprocess of: converting gilocculent-car-l bon black having adensity of about 3 pounds per cubic foot into substantially-sphericalgrains having a density oi about-30'pounds per cubic foot,

which consists in gradually spraying the surface of a mass of iiocculentcarbon black which is otherwise drywith a liquid, continuing thespraying step until a weight of liquid has been added not less than 66%nor more than 150% 01' the weight of the dry carbonblacl; treated,subjecting its particles to a turbulent agitation tocause the systematicand progressive building up d1:

rectly from thetreated mass of dry carbon particles upon the wettednuclei thereby producing,

amass of discrete spherical granuleshaving a 7 density of about 12pounds per cubic foot, then drying the product, and thensubiecting thedried product to turbulent. agitation and thereby increasing-its densityto substantially 30 pounds per cubic'ioot; a

11. The process 01' compacting iiocculent car-' bon black, whichconsists in gradually adding to dry carbon blacknot less-than 86% normore than 150% by weight of waterand'atthe same time stirring particlesoftheotherwlse dry mixture and thereby causing agglomeration jot theparticles directly from the treated maiisinto;

discrete granules of varylngsizes, and then drying saidgranules. H v

